Stretched poly(arylene thioether-ketone) films and production process thereof

ABSTRACT

Disclosed herein is a stretched poly(arylene thioether-ketone) film made of a thermoplastic material which comprises (A) 100 parts by weight of a melt-stable poly(arylene thioether-ketone) having predominant recurring units of the formula ##STR1## and having a melting point, Tm of 310°-380° C., a residual melt crystallization enthalpy, ΔHmc (420° C./10 min) of at least 10 J/g and a melt crystallization temperature, Tmc (420° C./10 min) of at least 210° C., and a reduced viscosity of 0.3-2 dl/g as determined by viscosity measurement at 25° C. and a polymer concentration of 0.5 g/dl in 98 percent by weight sufuric acid; and optionally, (B) up to 100 parts by weight of at least one of thermoplastic resins and/or up to 15 parts by weight of at least one of fillers. Its production process is also disclosed.

FIELD OF THE INVENTION

This invention relates to stretched films of a melt-stable poly(arylenethioether-ketone) (hereinafter abbreviated as "PTK") having predominantrecurring units of the formula ##STR2## in which the --CO-- and --S--are in the para position to each other, and more specifically tostretched films made of a thermoplastic material, which is composed ofthe melt-stable PTK alone or the melt-stable PTK and at least one ofother thermoplastic resins and/or at least one of fillers, and havinghigh heat resistance, strength and lubricity.

BACKGROUND OF THE INVENTION

With the advance of weight-, thickness- and length-reducing technologyin the field of the electronic and electric industry and with the recentadvancement of wight-reducing technology in the fields of theautomobile, aircraft and space industries, there has been a strongdemand for crystalline thermoplastic resins having heat resistance ofabout 300° C. or higher and permitting easy melt processing in recentyears.

As crystalline, heat-resistant, thermoplastic resins developed to date,there are, for example, poly(butylene terephthalate), polyacetal,poly(p-phenylene thioether) (PPS), etc. These resins are however unableto meet the recent requirement level for heat resistance.

Polyether ether ketones (PEEKs) and polyether ketones (PEKs) haverecently been developed as heat-resistant resins having a melting pointof about 300° C. or higher. These resins are crystalline thermoplasticresins. It has therefore been known that conventional melt processingtechniques such as extrusion, injection molding and melt spinning can beapplied to easily form them into various molded or formed articles suchas extruded products, injection-molded products, fibers and films. Theseresins however use expensive fluorine-substituted aromatic compoundssuch as 4,4'-difluorobenzophenone as their raw materials. Limitationsare thus said to exist to the reduction of their costs. It is alsopointed out that these resins involve a problem in expanding theirconsumption.

Based on an assumption that PTKs could be promising candidates forheat-resistant thermoplastic resins like PEEKs and PEKs owing to theirsimilarity in chemical structure, PTKs have been studied to some extentto date. There are some disclosure on PTKs, for example, in JapanesePat. Laid-Open No. 58435/1985 (hereinafter abbreviated as "PublicationA"), German Offenlegungsschrift 34 05 523A1 (hereinafter abbreviated as"Publication B"), Japanese Pat. Laid-Open No. 104126/1985 (hereinafterabbreviated as "Publication C"), Japanese Pat. Laid-Open No. 13347/1972(hereinafter abbreviated as "Publication D"), Indian J. Chem., 21A,501-502 (May, 1982) (hereinafter abbreviated as "Publication E"), andJapanese Pat. Laid-Open No. 221229/1986 (hereinafter abbreviated as"Publication F").

Regarding the PTKs described in the above publications, neither moldingnor forming has however succeeded to date in accordance withconventional melt processing techniques. Incidentally, the term"conventional melt processing techniques" as used herein means usualmelt processing techniques for thermoplastic resins, such as extrusion,injection molding and melt spinning.

The unsuccessful molding or forming of PTKs by conventional meltprocessing techniques is believed to be attributed to the poor meltstability of the prior art PTKs, which tended to lose theircrystallinity or to undergo crosslinking and/or carbonization, resultingin a rapid increase in melt viscosity, upon their melt processing.

It was attempted to produce some molded or formed products inPublications A and B. Since the PTKs had poor melt stability, certainspecified types of molded or formed products were only obtained by aspecial molding or forming process, where PTKs were used only as a sortof binder, being impregnated into a great deal of reinforcing fibers ofmain structural materials and molded or formed under pressure.

Since the conventional PTKs are all insufficient in melt stability asdescribed above, it has been unable to obtain formed products such asfilms by applying conventional melt processing techniques.

OBJECTS AND SUMMARY OF THE INVENTION

An object of this invention is to overcome the above-mentioned drawbacksof the prior art PTKs and hence to provide stretched films by using anovel melt-stable PTK which permits easy application of conventionalmelt processing techniques.

Another object of this invention is to provide stretched films havingheat resistance, strength and lubricity from a thermoplastic materialwhich is composed of the melt-stable PTK alone or the melt-table PTK andat least one of other thermoplastic resins and/or at least one offillers.

The present inventors started an investigation with a view toward usingeconomical dichlorobenzophenone and/or dibromobenzophenone as a rawmaterial for PTK without employing any expensive fluorine-substitutedaromatic compound. In addition, a polymerization process was designed inan attempt to conduct polymerization by increasing the water content inthe polymerization system to an extremely high level compared toprocesses reported previously, adding a polymerization aid and suitablycontrolling the profile of the polymerization temperature. As a result,it has been found that the above process can afford highmolecular-weight PTKs economically. The PTKs obtained by the above newprocess were however still dissatisfactory in melt stability. Thus, thepresent inventors made further improvements in the polymerizationprocess. It was then revealed that melt-stable PTKs, which permitted theapplication of conventional melt processing techniques, could beobtained by conducting polymerization without addition of anypolymerization aid while paying attention to the selection of a chargeratio of monomers, the shortening of the polymerization time at hightemperatures, the selection of a material for a polymerization reactor,etc. and if necessary, by conducting a stabilization treatment in afinal stage of the polymerization. It was also found that formedproducts such as films could be obtained easily from such melt-stablePTKs by general melt-processing methods.

Based on these findings, the present inventors has proceeded with afurther investigation on the production of stretched films. Theinvestigation has eventually resulted in the completion of the presentinvention.

In one aspect of this invention, there is thus provided a stretchedpoly(arylene thioether-ketone) film made of a thermoplastic materialwhich comprises:

(A) 100 parts by weight of a melt-stable poly(arylene thioether-ketone)having predominant recurring units of the formula ##STR3## wherein the--CO-- and --S-- are in the para position to each other, and having thefollowing physical properties (a)-(c):

(a) melting point, Tm being 310-380° C.;

(b) residual melt crystallization enthalpy, ΔHmc (420° C./10 min) beingat least 10 J/g, and melt crystallization temperature, Tmc (420° C./10min) being at least 210° C., wherein ΔHmc (420° C./10 min) and Tmc (420°C./10 min) are determined by a differential scanning calorimeter(hereinafter abbreviated as "DSC") at a cooling rate of 10° C./min,after the poly(arylene thioether-ketone) is held at 50° C. for 5 minutesin an inert gas atmosphere, heated to 420° C. at a rate of 75° C./minand then held for 10 minutes at 420° C.; and

(c) reduced viscosity being 0.3-2 dl/g as determined by viscositymeasurement at 25° C. and a polymer concentration of 0.5 g/dl in 98percent by weight sulfuric acid; and optionally,

(B) up to 100 parts by weight of at least one of thermoplastic resinsand/or up to 15 parts by weight of at least one of fillers.

In another aspect of this invention there is also provided a process forthe production of a stretched poly(arylene thioether-ketone) film, whichcomprises, upon processing the thermoplastic material into the stretchedpoly(arylene thioether-ketone) film, forming the thermoplastic materialinto an amorphous film, stretching, as first-stage stretching, theamorphous film to a draw ratio of from 1.5:1 to 7:1 in one direction at100-180° C. to give a birefringence of 0.05-0.35, stretching, asoptional second-stage stretching, the resultant film to a draw ratio offrom 1.5:1 to 7:1 in a direction perpendicular to said one direction at100-180° C., and then heat setting the resulting film at a temperatureof from 200° C. to a temperature just below the melting point of thepoly(arylene thioether-ketone).

In a further aspect of this invention, there is also provided a processfor the production of a stretched poly(arylene thioether-ketone) film,which comprises, upon processing the thermoplastic material into thestretched poly(arylene thioether-ketone) film, forming the thermoplasticmaterial into an amorphous film, stretching the amorphous film to a drawratio of from 1.5:1 to 7:1 simultaneously in both machine and transversedirections at 100-180° C. and then heat setting the resultant film at atemperature of from 200° C. to a temperature below the melting point ofthe poly(arylene thioether-ketone).

The present invention can therefore provide stretched films, which havehigh heat resistance, strength and lubricity, by using a PTK which hasmelt stability sufficient to apply general melt processing techniquesand also a high molecular weight.

DETAILED DESCRIPTION OF THE INVENTION

Features of the present invention will hereinafter be described indetail.

Chemical Structure of PTKs

The melt-stable PTKs according to the present invention are poly(arylenethioether-ketones) (PTKs) having predominant recurring units of theformula ##STR4## wherein the --CO-- and --S-- are in the para positionto each other. In order to be heat-resistant polymers comparable withPEEK and PEK, the PTKs usable for the practice of this invention maypreferably contain, as a main constituent, the above recurring units ina proportion greater than 50 wt.%, more preferably, of 60 wt.% orhigher, most preferably, of 70 wt.% or higher. If the proportion of therecurring units is 50 wt.% or less, there is a potential problem thatthe crystallinity of the polymer is reduced and its heat resistance isreduced correspondingly.

Exemplary recurring units other than the above recurring units mayinclude: ##STR5## (except for the recurring unit in which the --CO-- and--S-- are in the para position to each other.); ##STR6## wherein R meansan alkyl group having 5 or less carbon atoms and m stands for an integerof 0-4).

It is desirable that the melt-stable PTKs employed in this invention areuncured polymers, especially, uncured linear polymers. The term "cure"as used herein means a molecular-weight increasing treatment by a methodother than a usual polycondensation reaction, for example, by acrosslinking, branching or molecular-chain extending reaction,particularly, a molecular-weight increasing treatment by ahigh-temperature heat treatment or the like. In general, "curing" causesa PTK to lose or decrease its melt stability and crystallinity. Curingtherefore makes it difficult to employ conventional melt processing of aPTK. Even if a formed product such as a film is obtained, the producttends to have a low density and reduced crystallinity, in other words,may not be regarded as "a heat-resistant formed product" substantially.Curing is hence not preferred. However, PTKs having a partiallycrosslinked and/or branched structure to such an extent still allowingthe application of conventional melt processing techniques are stillacceptable as PTKs usable in the present invention. For example, PTKsobtained by conducting polymerization in the presence of a small amountof a crosslinking agent (e.g., polychlorobenzophenone,polybromobenzophenone or the like) and PTKs subjected to mild curing canbe regarded as melt-stable PTKs useful in this invention.

Physical Properties of PTKs

Summary of the physical properties:

The melt-stable PTKs useful in the practice of this invention have thefollowing physical properties.

(a) As indices of the characteristics of heat-resistant polymers, theirmelting points, Tm range from 310 to 380° C.

(b) As indices of the melt stability of polymers to which conventionalmelt processing techniques can be applied, their residual meltcrystallization enthalpies, ΔHmc (420° C./10 min) are at least 10 J/g,and their melt crystallization temperatures, Tmc (420° C./10 min) are atleast 210° C.

(c) In the case of extrusion products such as films, their shaping isdifficult due to drawdown or the like upon melt forming unless themolecular weight is sufficiently high. They should have a high molecularweight. As indices of the molecular weights of the polymers, theirreduced viscosities η_(red) should be within the range of 0.3-2 dl/g. Inthe present invention, each reduced viscosity η_(red) is expressed by avalue as determined by viscosity measurement at 25° C. and a polymerconcentration of 0.5 g/dl in 98 percent by weight sulfuric acid as asolvent.

(d) As indices of the characteristics of highly-crystalline polymers,the polymers have a density of at least 1.34 g/cm³ at 25° C. whenannealed at 280° C. for 30 minutes.

Details of the Physical Properties

(1) Heat resistance:

The melting point, Tm of a polymer serves as an index of the heatresistance of the polymer.

The PTKs useful in the practice of this invention have a melting point,Tm of 310-380° C., preferably 320-375° C., more preferably 330-370° C.Those having a melting point, Tm lower than 310° C. are insufficient inheat resistance as heat-resistant resins comparable with PEEKs and PEKs.On the other hand, it is difficult to perform the melt processing ofthose having a melting point TM higher than 380° C. withoutdecomposition. Such an excessively low or high melting point isundesired.

(2) Melt stability:

The greatest failure of the PTKs useful in the practice of thisinvention resides in that they have melt stability sufficient to permitthe application of conventional melt processing techniques.

All the conventional PTKs have low melt stability and ten to lose theircrystallinity or to undergo crosslinking or carbonization, resulting ina rapid increase in melt viscosity, upon their melt processing.

It is hence possible to obtain an index of the melt processability of aPTK by investigating the residual crystallinity of the PTK after holdingit at an elevated temperature of its melt processing temperature orhigher for a predetermined period of time. The residual crystallinitycan be evacuated equantitatively in terms of melt crystallizationenthalpy. Specifically, the residual melt crystallization enthalpy, ΔHmc(420° C./10 min) of the PTK and its melt crystallization temperature,Tmc (420° C./10 min) for the PTK which are determined by a DSC at acooling rate of 10° C./min, after the PTK is held at 50° C. for 5minutes in an inert gas atmosphere, heated to 420° C. at a rate of 75°C./min nd then held for 10 minutes at 420° C., can be used as measuresof its melt stability. In the case of a PTK having poor melt stability,it undergoes crosslinking or the like at the above high temperaturecondition of 420° C. and loses it crystallinity substantially.

The melt-stable PTKs of the present invention are polymers whoseresidual melt crystallization enthalpies, ΔHmc (b 420° C./10 min) arepreferably at least 10 J/g, more preferably at least 15 J/g, mostpreferably at least 20 J/g and whose melt crystallization temperatures,Tmc (b 420° C./10 min) are preferably at least 210° C., more preferablyat least 220° C., most preferably at least 230° C.

A PTK, whose ΔHmc (420° C./10 min) is smaller than 10 J/g or whose Tmc(420° C./10 min) is lower than 210° C., tends to lose its crystallinityor to induce a melt viscosity increase upon its melt processing, so thatdifficulties are encountered upon application of conventional meltprocessing techniques. It is hence difficult to form such a PTK into afilm.

(3) Molecular weight:

The solution viscosity, for example, reduced viscosity, η_(red) of apolymer can be used as an index of its molecular weight.

When a PTK or a composition thereof is melt-extruded into a film,drawdown or the like may occur as a problem upon its melt processing.

Therefore, the molecular weight which is correlated directly to the meltviscosity of the PTK is also an important factor for its meltprocessability.

In order to apply conventional melt processing techniques, highmolecular-weight PTKs whose reduced viscosities, η_(red) are preferably0.3-2 dl/g, more preferably 0.5-2 dl/g are desired. Since a PTK whoseη_(red) is lower than 0.3 dl/g has a low melt viscosity and hightendency of drawdown, it is difficult to apply conventional meltprocessing techniques. Further, the resulting stretched film isinsufficient in mechanical properties.

On the other hand, a PTK whose η_(red) exceeds 2 dl/g is very difficultto be produced and processed.

(4) Crystallinity:

As an index of the crystallinity of a polymer, its density is used.

The PTKs useful in the practice of this invention are desirably polymerswhose densities (at 25° C.) are preferably at least 1.34 g/cm³, morepreferably at least 1.35 g/cm³ when measured in a crystallized form byannealing them at 280° C. for 30 minutes. Those having a density lowerthan 1.34 g/cm³ have potential problems that they may have lowcrystallinity and hence insufficient heat resistance and their meltprocessability and the mechanical properties of resulting stretchedfilms ma also be insufficient.

In particular, PTKs crosslinked to a high degree (e.g., the PTKsdescribed in Publication A) have been reduced in crystallinity and theirdensities are generally far lower than 1.34 g/cm³.

Production Process of PTKs

The melt-stable PTKs useful in the practice of this invention can eachbe produced, for example, by subjecting alkali metal sulfide and adihalogenated aromatic compound, preferably, dichlorobenzophenone and/ordibromobenzophenone to dehalogenation and sulfuration, for a shortperiod of time, in the substantial absence of a polymerization aid (asalt of a carboxylic acid, or the like), in an aprotic polar organicsolvent, preferably, an organic amide solvent (including a carbamicamide or the like) and in a system having a water content far highercompared with conventionally-reported polymerization processes whilecontrolling the temperature profile suitably, and if necessary, bychoosing the material of a reactor suitably.

Namely, the melt-stable PTKs useful in the practice of this inventioncan each be produced suitably by polymerizing an alkali metal sulfideand a dihalogenated aromatic compound consisting principally ofdichlorobenzophenone and/or dibromobenzophenone by dehalogenation andsulfuration under the following conditions (a)-(c) in an organic amidesolvent.

(a) ratio of the water content to a change of the organic amide: 2.5-15(mole/kg);

(b) ratio of the amount of the charged dihalogenated aromatic compoundto the amount of the charged alkali metal sulfide: 0.95-1.2 (mole/mole);and

(c) reaction temperature: 60-300° C. with a proviso that the reactiontime at 210° C. and higher is within 10 hours.

The melt-stable PTKs can be obtained more suitably when a reactor atleast a portion of which, said portion being brought into contact withthe reaction mixture, is made of a titanium material.

Further, at least one halogen-substituted aromatic compound having atleast one substituent group having electron-withdrawing property atleast equal to --CO-- group (preferably, 4,4'-dichlorobenzophenoneand/or 4,4'-dibromobenzophenone employed as a monomer) may be added andreacted (as a stabilization treatment in a final stage of thepolymerization) so as to obtain PTKs improved still further in a meltstability.

The melt-stable PTKs employed in the present invention may preferably beuncured polymers as described above. They may however be PTKs in which acrosslinked structure and/or a branched structure has been incorporatedto a certain minor extent. In order to obtain a PTK with a branched orcrosslinked structure introduced therein, it is preferably to have apolyhalogenated compound, especially, a polyhalogenated benzophenonehaving at least three halogen atoms exist as a crosslinking agent in thepolymerization reaction system in such an amount that the charge ratioof the monomeric dihalogenated aromatic compound to the polyhalogenatedbenzophenone ranges from 100/0 to 95/5 (mole/mole). If the chargedamount of the polyhalogenated benzophenone is too much, physicalproperties of the resulting PTK, such as its melt processability,density and crystallinity, will be reduced. It is hence not preferableto charge such a polyhalogenated benzophenone too much.

Thermoplastic Resin

The thermoplastic material used as a raw material of a stretched film inthis invention may be composed of the melt-stable PTK alone. In view ofprocessability, physical properties, economy and the like, it may alsobe a resin composition obtained by mixing at least one of otherthermoplastic resins in an proportion of 0-100 parts by weight,preferably 0-90 parts by weight, and more preferably 0-80 parts byweight, all, per 100 parts by weight of the PTK. It is not preferable toadd the thermoplastic resin in any amount greater than 100 parts byweight, because such a high proportion results in an stretched film ofreduced heat resistance and strength.

As exemplary thermoplastic resins useful in the present invention, maybe mentioned resins such as poly(arylene thioethers), aromatic polyetherketones, e.g, PEEKs and PEKs, polyamides (including Aramids),polyamideimides, polyesters (including aromatic polyesters and liquidcrystalline polyesters), polysulfones, polyether sulfones, polyetherimides, polyarylenes, poly(phenylene ethers), polycarbonates, polyestercarbonates, polyacetals, fluoropolymers, polyolefins, polystyrenes,polymethyl methacrylate, and ABS; as well as elastomers such asfluororubbers, silicone rubbers, olefin rubbers, acrylic rubbers,polyisobutylenes (including butyl rubber), hydrogenated SBR, polyamideelastomers and polyester elastomers.

Those thermoplastic resins may be used either singly or in combination.

Among the above-exemplified thermoplastic resins, poly(arylenethioethers), especially, poly(arylene thioethers) having predominantrecurring units of the formula ##STR7## (hereinafter abbreviated as"PATEs"; said recurring units accounting for at least 50 wt. %) arepreferred, because their blending can provide stretched films which havemechanical properties at room temperature improved over those obtainedfrom the PTK alone and also heat resistance improved over those obtainedfrom the PATEs alone and are well-balanced in heat resistance,mechanical properties and flow characteristics.

Among the above-described thermoplastic resins, aromatic polyetherketones can improve the drawdown, mechanical properties (toughness inparticular), melt stability at the time of melt processing, etc. of thePTKs when blended with the latter. Although aromatic polyether ketonesinvolve such problems as high prices and difficult forming andprocessing (i.e., have poor flow characteristics), it is feasible toimprove their flow characteristics and heat resistance by blending themwith the PTKs. As a further advantage, the blending of such an aromaticpolyether ketone provides stretched films which are also attractiveeconomically. As illustrative examples of the aromatic polyether ketone,PEKs and PEEKs may be mentioned.

Filler:

In this invention, at least one of fillers and/or at least one ofinorganic fillers may be added in a proportion up to 15 parts by weightper 100 parts by weight of the PTK as desired. If the proportion of thefiller exceeds 15 parts by weight, there is a potential problem that theprocessability may be deteriorated to a considerable extent and thephysical properties of the resulting stretched films would bedeteriorated.

As exemplary fibrous fillers usable in this invention, may be mentionedfibers such as glass fibers, carbon fibers, graphite fibers, silicafibers, alumina fibers, zirconia fibers, silicon carbide fibers andAramid fibers; as well as whiskers such as potassium titanate whiskers,calcium silicate (including wollastonite) whiskers, calcium sulfatewhiskers, carbon whiskers, silicon nitride whiskers and boron whiskers.

As exemplary inorgainc fillers, may be mentioned talc, mica, kaolin,clay, silica, alumina, silica-alumina, titanium oxide, iron oxides,chromium oxide, calcium carbonate, calcium silicate, calcium phosphate,calcium sulfate, magnesium carbonate, magnesium phosphate, silicon,carbon (including carbon black), graphite, silicon nitride, molybdenumdisulfide, glass, hydrotalcite, ferrite, samarium-cobalt,neodium-iron-boron, etc., all, in a powder form.

These fibrous fillers and inorganic fillers may be used either singly orin combination.

Optional Components:

In the present invention, it is also possible to add one or moreadditives such as stabilizer, anticorrosive, lubricant,surface-roughening agent, ultraviolet absorbent, nucleating agent,mold-releasing agent, colorant, coupling agent and/or antistatic agent,as needed.

Production Process of Stretched Film

The stretched film of this invention can be produced by melt-forming athermoplastic material, which is composed of the melt-stable PTK aloneor a composition formed of 100 parts by weight of the PTK and up to 100parts by weight of at least one of thermoplastic resins and/or up to 15parts by weight of at least one of fillers, into a film by usual T-dieextrusion (an extrusion method making use of a T-die), inflation (anextrusion method employing a ring die), hot pressing or the like,stretching the film, and then heat setting the thus-stretched film.

Described specifically, a substantially amorphous film is obtained firstof all, for example, by charging the thermoplastic material into anextruder fitted with a T-die or ring die in the air or an inert gasatmosphere, melt-forming the thermoplastic material at 320-430° C. intoa film and then quenching the film or by pressing and forming thethermoplastic material into a film by a hot pressing machine whileheating and melting it at 320-430° C. and then quenching the film.Incidentally, the term "amorphous film" as used herein means astretchable film at the temperature around the glass transition point.The ratio ΔSTc/ΔSTm should be at least 0.1, where ΔSTc is the enthalpyupon crystallization when the amorphous film is heated at a rate of 10°C./min from room temperature by using a differential scanningcalorimeter (DSC), ΔSTm is also the enthalpy on melt when the film isheated in the above manner.

Where the amorphous film is obtained from the thermoplastic materialcomposed of the melt-stable PTK and the thermoplastic resin and twoendothermic peaks and two exothermic peaks occur upon melting of itscrystals and its crystallization respectively, it is possible to usevalues which are obtained by adding enthalpies corresponding to therespective heat quantities.

Such an amorphous film can be obtained by quenching a molten film at acooling rate of at least 200° C./min with a cooling medium such as wateron a cooling drum. Unless an amorphous film is used, stretching aroundthe glass transition temperature is difficult.

Incidentally, when an extruder such as that equipped with a T-die isused, it is preferred that the extruder is made of a non-ferrouscorrosion-resistant material at portions where it is brought intocontact with a molten resin. It is also preferred that the extruder isvented.

Next, the amorphous film obtained in the above-described manner isstretched to draw ratio of from 1.5:1 to 7:1 in one direction, i.e., auniaxial direction or in one direction and another directionperpendicular to said one direction, i.e., biaxial directions at100-180° C. by a stretching machine of the roll or stenter type or asimilar type or by a similar machine. When stretching the amorphous filmin biaxial directions, the stretching may be performed by eithersequential or simultaneous biaxial stretching.

In the case of uniaxial stretching, the stretching in one direction iseffected at a draw ratio of from 1.5:1 to 7:1, preferably, from 2:1 to6:1 at 100-180° C., preferably, 120-160° C. to make the birefringence ofthe film fall within the range of from 0.05 to 0.35 and the resultingfilm is thereafter heat set at a temperature of from 200° C. to atemperature just below the melting point of the PTK. If the temperatureis lower than 100° C. here, the stretching is difficult to perform andmoreover, substantial tearing takes place. At temperatures over 180° C.,the film is rendered brittled due to its crystallization and significanttearing also takes place. On the other hand, the draw ratio may suitablybe in the range of from 1.5:1 to 7:1 in view of the degree oforientation of the film and the tearing of the film. The speed of thestretching may preferably be in a range of 10-10,000 %/min.

When sequential biaxial stretching is performed, the first-stagestretching is effected as in the above uniaxial stretching, namely, at100-180° C., preferably, 120-160° C. and at a draw ratio of 1.5:1 to7:1, preferably, 2:1 to 6:1 so as to make the birefringence of the filmfall within a range of from 0.05 to 0.35. As the second stretching, theresultant film is then stretched at 100-180° C., preferably, 120-160° C.to a draw ratio of from 1.5:1 to 7:1, preferably, from 2:1 to 6:1 in adirection perpendicular to the stretching direction of the first-stagestretching, followed by heat setting at a temperature of from 200° C. tothe melting point of the PTK. If the temperature of the second-stagestretching is lower than 100° C., the stretching is difficult to performand substantial tearing of the film takes place. If it exceeds 180° C.on the contrary, the film is rendered brittle due to its crystallizationand again, substantial tearing of the film occurs. The draw ratio of thesecond-stage stretching may suitably be in a range of from 1.5:1 to 7:1in view of the degree of orientation of the film and the tearing of thefilm. The speed of the second-stage stretching may preferably be in arange of 10-10,000 %/min.

In the case of simultaneous biaxial stretching, the stretching isperformed at 100-180° C., preferably, 120-160° C. and at a draw ratio of1.5:1 to 7:1, preferably, 2:1 to 6:1 in both machine and transversedirections. Here, the birefringence of the film ranges from 0 to 0.35.After the stretching, the resultant film is heat set at a temperature offrom 200° C. to the melting point of the PTK. If the stretchingtemperature is lower than 100° C., it is not preferable because it maycause the film to split or whiten. At temperatures higher than 180° C.on the other hand, the film tends to crystallize either before or duringits stretching so that the stretching of the film becomes difficult andthe film is susceptible to breakage. If the draw ratio is smaller than1.5:1, it is only possible to obtain films insufficient in mechanicalproperties such as strength and modulus. It the film is stretched to adraw ratio greater than 7:1, the film is whitened and/or tornconsiderably.

The heat set may be performed at a temperature of from 200° C. to atemperature just below the melting point of the PTK, preferably, in arange of 250-330° C., for 1-3,000 seconds, more preferably, 5-2,500seconds while being restrained from shrinkage under stress (tension) tothe film and limiting its deformation within ±20%. After the heat set,the film may be subjected to thermal relaxation at 200-360° C.,substantially under no stress, for 1-3,000 seconds, preferably, 5-2,000seconds as needed. The density of the stretched film is increased by theheat set, so that the density (25° C.) of PTK portions reaches at least1.34 g/cm² and its heat resistance, dimensional stability, mechanicalstrength and the like are also improved.

Further, in order to obtain a stretched film having practical utility,it is necessary in a uniaxially stretched film to make the birefringence(the difference between the refractive in the stretched direction andthat in a direction perpendicular to the stretched direction) fallwithin the range of from 0.05 to 0.35. If the birefringence is smallerthan 0.05, sufficient strength cannot be obtained at elevatedtemperatures. If it is greater than 0.35 on the contrary, the film tendsto undergo splitting and in addition, is whitened to fail to providesufficient strength when the film is heat-treated. After theabove-described stretching, the film may optionally be stretchedfurther, as a second-stage stretching, in a direction perpendicular tothe direction of the previous stretching. If the birefringence issmaller than 0.05, the film may be wrinkled or rendered brittle in thesubsequent heat treatment. If the birefringence exceeds 0.35, the filmmay be whitened or in some instances, undergoes splitting to render thestretching no longer feasible in the second-stage stretching.Birefringences outside the above range are therefore not preferred. Inorder to control the birefringence of the uniaxially-stretched filmwithin the above range, the stretching must be performed under theabove-mentioned conditions.

A high-lubricity film having a coefficient of surface dynamic frictionof 0.7 or smaller can be obtained, for example, by adding a small amountof an inorganic filler such as calcium carbonate, kaolin, clay, alumina,silica or titanium oxide to the melt-stable PTK or to the composition ofthe melt-stable PTK and at least one of other thermoplastic resins andthen forming the resultant mixture into a film, by treating both sidesof an unstretched film with an organic solvent having high compatibilitywith the PTK and then stretching it, or by roughening one or bothsurfaces of a stretched film by sand blasting or surface-rougheningrolls.

Physical Properties of Stretched Film

The stretched film of this invention generally has an average thicknessof 0.1-3,000 μm, preferably, 1-2,000 μm and has the following excellentphysical properties:

(a) density of PTK portions being at least 1.34 g/cm³ at 25° C.;

(b) tensile strength being at least 5 kg/mm² at 23° C. or at least 1kg/mm² at 270° C.;

(c) tensile modulus being at least 200 kg/mm² at 23° C. or at least 5kg/mm² at 270° C.;

(d) temperature of 10-seconds solder heat resistance being at least 280°C.; and

(e) coefficient of surface dynamic friction being 0.7 or smaller.

Measurements of physical properties

Density of PTK portions (25° C.):

Where the thermoplastic material as the raw material of the film iscomposed of the PTK alone, the density (25° C.) of PTK portions is thesame as the density (25° C.) of the stretched film. Where thethermoplastic material contains the thermoplastic resin and/or filler inaddition to the PTK, a sample is separately prepared under the sameconditions for the production of the stretched film by using the samethermoplastic material except for the omission of the PTK, and thedensity (25° C.) of PTK portions can be determined from the density (25°C.) of the stretched film and the density (25° C.) of the sample free ofthe PTK. ##EQU1##

Tensile strength: ASTM-D638.

Tensile modulus: ASTM-D638.

Solder heat resistance:

The solder heat resistance is expressed in terms of the highesttemperature of a bath of molten solder at which temperature a stretchedfilm does not develop marked changes in external appearance such asblister, wrinkles and shrinkage even when dipped for 10 seconds in thebath.

Coefficient of sufface dynamic friction: ASTM-D1894. The coefficient ofsurface dynamic friction of the stretched film is measured at 25° C.against another stretched film of the same kind as the first-mentionedstretched film.

As described above, the stretched PTK film of this invention is a filmobtained by using a melt-stable PTK having a high molecular weight of0.3-2 dl/g in terms of reduced viscosity, a density of 1.34 g/cm³ whenannealed at 280° C. for 30 minutes and a melting point Tm of 310-380° C.The stretched PTK film thus has high heat resistance and strength.

Application Fields

The stretched films of this invention can be used in a wide variety offields, for example, as base films for magnetic recording materials(including films for vacuum deposition or sputtering and magneticrecording films of the perpendicular magnetization type), films forcapacitors (especially, films for chip-type capacitors), printed circuitboards (including both flexible and rigid types), insulating films,printer tapes, stampable sheets, various trays, containers, etc.

ADVANTAGES OF THE INVENTION Stretched PTK films having high heatresistance, strength and lubricity were successfully obtained by thepresent invention. PTKs according to conventional techniques had poormelt stability, so that melt processing was not applicable thereto.Owing to the use of the novel melt-stable PTK in this invention, meltprocessing and stretching have both become feasible and stretched PTKfilms having excellent physical properties have been provided.

The stretched PTK films according to this invention can be used in awide variety of fields in which heat resistance, strength and lubricityare required.

EMBODIMENTS OF THE INVENTION

The present invention will hereinafter be described specifically by thefollowing Examples, Comparative Examples and Experiments. It shouldhowever be borne in mind that the scope of the present invention is notlimited to the following Examples and Experiments.

Experiments Synthesis Experiment 1 (Synthesis of Melt-stable PTK)

A titanium-lined reactor was charged with 90 moles of4,4'-dichlorobenzophenone (hereinafter abbreviated as "DCBP"; product ofIhara Chemical Industry Co., Ltd.), 90 moles of hydrated sodium sulfide(water content: 53.6 wt.%; product of Sankyo Kasei Co., Ltd.) and 90 kgof N-methylpyrrolidone (hereinafter abbreviated as "NMP") (watercontent/NMP =5.0 moles/kg). After the reactor being purged with nitrogengas, the resultant mixture was heated from room temperature to 240° C.for 1.5 hours and then maintained at 240° C. for 2.5 hours. In order toapply the final-stage treatment of the polymerization, the reactionmixture was heated to 260° C. over 1 hour while charging under pressurea mixture composed of 9.0 moles of DCBP, 15 kg of NMP and 75 moles ofwater. The resultant mixture was maintained further at 260° C. for 0.3hour to react them.

The reactor was cooled, and the reaction mixture in the form of a slurrywas taken out of the reactor and was then poured into about 200 l ofacetone. The resultant polymer was precipitated. The polymer wascollected by filtration, and then washed twice with acetone andadditionally twice with water. Acetone and water were removed to obtainthe polymer in a wet form. The wet polymer was dried at 80° C. for 12hours under reduced pressure, thereby obtaining Polymer P1 as powder.

Synthesis Experiment 2 (Synthesis of Melt-stable PTK)

A titanium-lined reactor was charged with 90 moles of DCBP, 0.9 mole ofp-dibromobiphenyl, 90 moles of hydrated sodium sulfide (water content:53.6 wt.%) and 90 kg of NMP (water content/NMP=5.0 moles/kg). After thereactor being purged with nitrogen gas, the resultant mixture was heatedfrom room temperature to 240° C. over 1.5 hours and then maintained at240° C. for 2.5 hours. The reaction mixture in the form of a slurry wasprocessed in the same manner as in Synthesis Experiment 1, therebyobtaining Polymer P2 as powder.

Measurement of Physical Properties Measurement of melting points

With respect to each of the PTKs thus obtained, the melting point Tm wasmeasured as an index of its heat resistance. The measurement wasperformed in the following manner. About 10 mg of each PTK (powder) wasweighed. Using a differential scanning calorimeter (Model TC10A;manufactured by Mettler Company), the sample was held at 50° C. for 5minutes in an inert gas atmosphere and was then heated at a rate of 10°C./min so as to measure its melting point.

Measurement of residual melt crystallization enthalpies

With respect to each of the PTKs thus obtained, the residual meltcrystallization enthalpy ΔHmc (420° C./10 min) and the meltcrystallization temperature, Tmc (420° C./10 min) were measured as anindex of its melt stability. Namely, the temperature corresponding to apeak of melt crystallization measured by the DSC is represented by Tmc(420° C./10 min) and the amount of heat converted from the area of thepeak was taken as residual melt crystallization enthalpy, ΔHmc (420°C./10 min). Described specifically, about 10 mg of each PTK (powderform) was weighed. After holding the PTK at 50° C. for 5 minutes in aninert gas atmosphere, it was heated at a rate of 75° C./min up to 420°C. and held at that temperature for 10 minutes. While cooling the PTK ata rate of 10° C./min, its ΔHmc (420° C./10 min) and Tmc (420° C./10 min)were measured. Results are collectively shown in Table 1.

Measurements of densities and solution viscosities

As indices of crystallinity of the PTKs, their densities were measured.Namely, each PTK (powder) was first of all placed between two polyimidefilms ("Kapton", trade mark; product of E. I. du Pont de Nemours & Co.,Inc.). It was preheated at 385° C. for 2 minutes and then press-formedat 385° C. for 0.5 minute by a hot press. It was then quenched to obtainan amorphous sample whose thickness was about 0.15 mm. A part of theamorphous sheet was used directly as a sample, while the other part wasannealed at 280° C. for 30 minutes to use it as an annealed sample withan increased degree of crystallinity. Their densities were measured at25° C. by means of a density gradient tube(lithium bromide/water). Asindices of the molecular weights of the PTKs, their solution viscosities(reduced viscosities η_(red)) were measured.

Namely, each PTK sample was dissolved in 98 wt.% sulfuric acid to give apolymer concentration of 0.5 g/dl. The reduced viscosity of theresultant solution was then measured at 25° C. by means of a Ubbellohdeviscometer.

Measurement results of the respective physical properties are showncollectively in Table 1.

                  TABLE 1                                                         ______________________________________                                                        Example                                                                       Synthesis                                                                              Synthesis                                                            Experiment 1                                                                           Experiment 2                                         ______________________________________                                        Heat resistance                                                               Tm (°C.)   366        365                                              Melt stability                                                                ΔHmc (420° C./10 min) (J/g)                                                        56         43                                               Tmc (420° C./10 min) (°C.)                                                        306        290                                              Density (25° C.)                                                       Amorphous film    1.30       1.30                                             Annealed film     1.35       1.35                                             Molecular weight                                                              η.sub.red (dl/g)                                                                            0.81       0.61                                             Remarks Polymer No.   P1         P2                                           ______________________________________                                    

EXAMPLE 1

Under a nitrogen gas stream, Polymer P1 was charged into a smallextruder equipped with a T-die. It was melt-extruded at 375° C. and thenquenched on a cooling roll, thereby producing an amorphous film havingan average thickness of 150 μm.

In the above operation, the temperature of the cooling roll was 50° C.,the distance between the tip of the T-die and the cooling roll was about1 cm, and the flow rate of resin from the tip of the T-die was 30cm/min. Therefore, the external cooling rate of the molten resin filmwas at least 200° C./min.

In addition, the ratio ΔSTc/ΔSTm to the enthalpy upon crystallizationwhen the film it is heated at a rate of 10° C./min by using a DSC to theenthalpy on melt when the film is heated in the above manner was 0.29.

The amorphous film thus produced from P1 was stretched to a draw ratioof 5:1 in one direction at 155° C. by using a tension (manufactured byBoldwin Company). The birefringence of the stretched film was 0.28. Itwas then heat set at 310° C. for 5 minutes while maintaining its lengthconstant. It was thereafter subjected to thermal relaxation at 290° C.for 5 minutes under no stress, whereby a uniaxially-stretched film(Stretched Film 1) was produced.

Measurement of birefringence

The birefringence of each uniaxially-stretched film was determined bymeasuring the retardation (the amount of delay between the speed oflight along the axis of orientation of the film and that in a directionperpendicular to the axis of the orientation) and then using theequation, retardation =(film thickness) × (birefringence). Where theretardation of a sample film is large and its measurement is difficult,the retardation of the sample film is measured in a reduced state byprecisely superposing a film having a known retardation value at rightangle on the sample film. The known retardation value of the superposedfilm is thereafter added to a retardation value thus measured, so thatthe retardation value of the sample film is determined. Thebirefringence of the uniaxially-stretched film is then determined bydividing the thus-obtained retardation value thereof with its thickness.

EXAMPLE 2

The amorphous film produced from Polymer P1 in Example 1 was stretchedto a draw ratio of 3:1 in the machine direction at 155° C. asfirst-stage stretching by a biaxial stretching testing machine(manufactured by Toyo Seiki Seisakusho, Ltd.). The birefringence of thefilm was 0.19. It was then stretched to a draw ratio of 2.9:1 in thetransverse direction at 157° C. as second-stage stretching, heat set at310° C. for 5 minutes while maintaining the length and then subjected tothermal relaxation at 290° C. for 5 minutes under no stress, therebyproducing a biaxailly-stretched film (Stretched Film 2).

EXAMPLE 3

The amorphous film produced from Polymer P1 in Example 1 was biaxiallystretched to a draw ratio of 3.2:1 in the machine direction and at thesame time, to a draw ratio of 3.2:1 in the transverse direction at 156°C. by the biaxial stretching testing machine used in Example 2. Thethus-obtained film as heat set at 320° C. for 5 minutes whilemaintaining its length constant, thereby producing a biaxially-orientedfilm (Stretched Film 3).

Physical properties of the individual stretched films are shown in Table2.

                                      TABLE 2                                     __________________________________________________________________________                   Example 1                                                                           Example 2                                                                             Example 3                                        __________________________________________________________________________    Polymer No. of PTK                                                                           P1    P1      P1                                               Draw ratio (machine/                                                          transverse)**  5:1/--                                                                              3:1/2.9:1                                                                             3.2:1/3.2:1                                      Density (25° C.)* (g/cm.sup.3)                                                        1.36  1.36    1.36                                             Tensile strength (machine/                                                    transverse)**                                                                 23° C. (kg/mm.sup.2)                                                                  21/-- 16/15   --/18                                            270° C. (kg/mm.sup.2)                                                                 17/-- 10/8    --/11                                            Tensile modulus (machine/                                                     transverse)**                                                                 23° C. (kg/mm.sup.2)                                                                  560/--                                                                              390/380 --/420                                           270° C. (kg/mm.sup.2)                                                                 70/-- 30/20   --/40                                            Solder heat resistance (°C.)                                                          >310  >310    >310                                             Remarks                                                                            Stretched Film No.                                                                      Stretched                                                                           Stretched                                                                             Stretched                                                       Film 1                                                                              Film 2  Film 3                                                Stretching method                                                                       Uniaxial                                                                            Biaxial Biaxial                                                               (Sequential)                                                                          (Simultaneous)                                   __________________________________________________________________________     *Density gradient tube method in lithium bromide/water system.                **In "(machine/transverse)" used in the table, "machine" means the            stretching direction (MD) in the firststage stretching and "transverse"       denotes the stretching direction (TD) in the secondstage stretching.     

EXAMPLE 4

In a Henschel mixer, 1 part by weight of titanium oxide powder and 1part by weight of silica powder were mixed well with 100 parts by weightof Polymer P1 to obtain a blend.

The blend was charged under a nitrogen gas stream into a single-screwextruder having a cylinder diameter of 40 mm and a cylinder length of 1m and equipped with a nozzle having a diameter of 5 mm. It was extrudedat 375° C. into strands. The strands were quenched and chopped intopellets. The thus-obtained pellets were heat-treated for 3 hours in anoven of 160° C.

Using those pellets, a biaxially-stretched film was produced in the samemanner as in Example 2. The birefringence of the uniaxially-stretchedfilm before the second-stage stretching was 0.18. The coefficient ofsurface dynamic friction of the thus-obtained biaxially-stretched filmwas 0.45 as measured at 25° C. against another stretched film of thesame kind as the biaxially-stretched film in accordance with the testingmethod of ASTM-D1894. It was therefore a high-lubricity film.

EXAMPLES 5-7

Polymer P2 were charged under a nitrogen gas steam into a smalltwin-screw extruder equipped with a nozzle having a diameter of 3 mm. Itwas extruded into strands at 370° C. and an extrusion rate of about 1.6kg/hour. After cooling, the strands were formed into pellets. Thethus-obtained pellets were heat-treated for 4 hours in an oven of 155°C. Using an extruder which was equipped with a T-die having a lipclearance of 0.5 mm and a width of 250 mm and had a cylinder diameter of35 mm and an L/D ratio of 28, the above pellets were melt-extruded. Thetemperature of the molten resin was 370° C. The molten film wasimmediately quenched on a metal roll of 79° C. by applying a staticpotential of 5 KV via a pinning apparatus (casting). Since the resintemperature was 370° C. at the die lip outlet, the flow rate of theresin was 21 cm/min and the distance from the tip of the die lip to thepoint of contact of the resin with the metal roll (cast roll) was about1 cm, the external cooling rate of the resin was at least 200° C./min.

An amorphous film (ΔSTc/ΔSTm=0.31) which had been obtained by effectingquenching in the above manner was uniaxially and continuously stretchedvia guide rolls. The stretching temperature was 145° C. in terms of thesurface temperature of stretching roll. The draw ratio was 2.5:1. Thebirefringence of the thus-obtained film was 0.16. Theuniaxially-stretched film was then biaxially stretched and heat set by astenter biaxial stretching machine which was controlled at a stretchingtemperature of 136° C. and a heat setting temperature of 290° C. Thedraw ratio was 3:1 and the relaxation ratio was 5%. The travelling speedof the film inside the stenter was 3.5 m/min and the thickness of theresultant film was 12 μm.

(EXAMPLE 5)

Portions of the thus-obtained film were respectively held between squaremetal frames having a length of 30 cm per side to fix the films alongthe entire peripheries thereof. The films were thereafter heat set underthe following conditions while maintaining the lengths of the filmsconstant, so that two kinds of films were produced, one being a filmheat set for 10 minutes in an oven controlled at 300° C. (Example 6) andthe other a film heat set for 10 minutes in an oven controlled at 340°C. (Example 7).

Physical properties of the thus-obtained films are shown in Table 3.

                                      TABLE 3                                     __________________________________________________________________________    Physical properties of film                                                   Tensile strength                                                                           Elongation                                                                              Tensile modulus in                                                                      Density                                                                            Solder heat                             machine/transverse*                                                                        machine/transverse*                                                                     machine/transverse*                                                                     (25° C.)                                                                    resistance                              (23° C.) (kg/mm )                                                                   (23° C.) (%)                                                                     (23° C.) (kg/mm )                                                                (g/cm )                                                                            (°C.)                            __________________________________________________________________________    Ex. 5                                                                            16/17     29/30     300/300   1.35 >285                                    Ex. 6                                                                            15/17     26/24     290/290   1.36 >300                                    Ex. 7                                                                            13/15     12/17     320/330   1.36 >310                                    __________________________________________________________________________     *In "(machine/transverse)" used in the table, "machine" means the             stretching direction (MD) in the firststage stretching and "transverse"       denotes the stretching direction (TD) in the secondstage stretching.     

COMPARATIVE EXAMPLE 1

The amorphous film obtained in Example 5 was simultaneously andbiaxially stretched to a draw ratio of 3:1 in the machine direction andto a draw ratio of 3:1 in the transverse direction at 145° C. by thebiaxial stretching testing machine used in Example 2. The thus-obtainedfilm was heat set at 180° C. for 10 minutes while maintaining its lengthconstant.

The solder heat resistance of the film was not than 280° C.

EXAMPLES 8-10

Using Polymer P1, pellets were obtained in the same manner as in Example5. In addition, stretched films (thickness: 12 μm) were separatelyproduced by the same extruder and stretching machine as those employedin Example 5 under the extrusion and film-forming conditions given inTable 4.

Those extrusion and film-forming conditions are physical properties ofthe stretched films are collectively shown in Table 4.

                                      TABLE 4                                     __________________________________________________________________________                                 Example 8                                                                           Example 9                                                                           Example 10                           __________________________________________________________________________    Melt extrusion                                                                            Melt extrusion temperature (°C.)                                                        370   370   370                                              Output (kg/hour) 1.5   2.0   2.0                                  Casting     Casting roll temperature (°C.)                                                          80    120   75                                               Die lip - casting roll distance (mm)                                                           10    10    10                                               Pinning voltage (KV)                                                                           5     3     4.8                                              Cooling rate (°C./min)                                                                  >200  >200  >200                                 First-stage stretching                                                                    Preheating temperature (°C.)                                                            95    100   80                                               Preheating time (sec)                                                                          60    60    60                                               Stretching temperature (°C.)                                                            145   140   150                                              Draw ratio       2.0:1 3.0:1 2.5:1                                            Birefringence    0.12  0.20  0.18                                 Second-stage stretching                                                                   Stretching temperature (°C.)                                                            130   140   135                                              Draw ratio       2.5:1 3.3:1 3.5:1                                Heat set    Temperature (°C.) × Time (sec)                                                    300 × 300                                                                     330 × 60                                                                      320 × 120                      Physical properties of                                                                    Tensile strength (23° C.)                                  film        (kg/mm.sup.2)    12/14 17/18 16/21                                (machine/transverse)*                                                                     Tensile modulus (23° C.)                                               (kg/mm.sup.2)    250/270                                                                             350/320                                                                             360/380                                          (machine/transverse)*                                                         Density (25° C.) (g/cm.sup.3)                                                           1.35  1.36  1.35                                             Solder heat resistance (°C.)                                                            > 290 >310  >310                                 __________________________________________________________________________     *In "(machine/transverse)" used in the table, "machine" means the             stretching direction (MD) in the firststage stretching (MD) and               "transverse" denotes the stretching direction (TD) in the secondstage         stretching.                                                              

EXAMPLE 11

After mixing 80 parts by weight of Polymer P2 and 20 parts by weight ofpoly(paraphenylene thioether) (product of Kureha Chemical Industry Co.,Ltd.; melt viscosity: 6800 poises at 310° C. and a shear rate of 200sec⁻¹) at room temperature in a Henschel mixer, pellets were formed inthe same manner as in Example 5. In the same manner as in Example 5, thepellets were heat-treated for 2 hours in an oven of 170° C. and a moltenfilm was extruded and quenched to obtain an amorphous film (coolingrate: at least 200° C./min, ΔSTc/ΔSTm=0.30). The film was simultaneouslyand biaxially stretched to a draw ratio of 3:1 in the machine directionand to a draw ratio of 3:1 in the transverse direction at 150° C. in thesame manner as in Example 3. (stretching speed: 2,000 %/min).

The thickness of the resultant film was 11 μm. The biaxially-stretchedfilm was held on a metal frame to secure it along the entire peripherythereof, and was then heat set at 320° C. for 5 minutes whilemaintaining its length constant.

The tensile strength (23° C.), elongation (23° C.) and tensile modulus(23° C.) of the film were 20 kg/mm², 30% and 340 kg/mm² respectively. Inaddition, its solder heat resistance was at least 310° C., and thedensity of its PTK portions was 1.36 g/cm³.

EXAMPLE 12

After mixing 60 parts by weight of Polymer P2 and 40 parts by weight ofPATE at room temperature in a Henschel mixer, pellets were produced inthe same manner as in Example 5.

The pellets were heat-treated for 4 hours in an oven of 155° C.Following the procedure of Example 5, a molten film was extruded andthen quenched into an amorphous film (cooling rate: at least 200°C./min, ΔSTc/ΔSTm=0.30).

Using the film, a stretched film was produced in the same manner as inExample 5 (film thickness: 15 μm). Upon production of the stretchedfilm, the following film-processing conditions were employed.

    ______________________________________                                        First-stage stretching:                                                       Stretching temperature:                                                                              144° C.                                         Draw ratio:            3:1                                                    Birefringence:         0.17                                                   Second-stage stretching:                                                      Stretching temperature:                                                                              127° C.                                         Draw ratio:            3.3:1                                                  Heat set:                                                                     Temperature:           290° C.                                         Time:                  300 seconds                                            Relaxation ratio:      5%                                                     ______________________________________                                    

The tensile strength (machine/transverse) (23° C.), elongation(machine/transverse) (23° C.) and tensile modulus (machine/transverse)(23° C.) of the film were 18/21 kg/mm², 25/23% and 330/350 kgrespectively. Its solder heat resistance was at least 285° C., while thedensity of its PTK portions was 1.36 g/cm³. Here, in the term"(machine/transverse)" used above, "machine" means the stretchingdirection (MD) in the first-stage stretching and "transverse" denotesthe stretching direction (TD) in the second-stage stretching.

EXAMPLE 13

After mixing 60 parts by weight of Polymer P2 and 40 parts by weight ofPEEK (product of Imperial Chemical Industries Ltd.) at room temperaturein a Henschel mixer, pellets were produced in the same manner as inExample 5. The pellets were heat-treated for 2 hours in an oven of 170°C. Following the procedure of Example 5, a molten film was extruded andthen quenched into an amorphous film (cooling rate: at least 200°C./min, ΔSTc/ΔSTm=0.30).

In the same manner as in Example 3, the film was biaxially andsimultaneously stretched to a draw ratio of 3:1 in the machine directionand to a draw ratio of 3:1 in the transverse direction at 154° C.,thereby obtaining a film whose thickness was 12 μm.

The biaxially-stretched film was held on a metal frame to secure italong the entire periphery thereof, and was then heat set at 330° C. for10 minutes while maintaining its length constant.

The tensile strength (23° C.), elongation (23° C.) and tensile modulus(23° C.) of the film were 21 kg/mm², 35% and 400 kg/mm² respectively. Inaddition, its solder heat resistance was at least 320° C., and thedensity of its PTK portions was 1.36 g/cm³.

We claim:
 1. A stretched poly(arylene thioether-ketone) film made of athermoplastic material which comprises:(A) 100 parts by weight of amelt-stable poly(arylene thioether-ketone) having predominant recurringunits of the formula ##STR8## wherein the --CO-- and --S-- are in thepara position to each other, and having the following physicalproperties (a)-(c):(a) melting point, Tm being 310-380° C.; (b) residualmelt crystallization enthalpy, ΔHmc (420° C./10 min) being at least 10J/g, and melt crystallization temperature, Tmc 420° C./10 min) being atleast 210° C., wherein ΔHmc (420° C./10 min) and Tmc (420° C./10 min)are determined by a differential scanning calorimeter at a cooling rateof 10° C./min, after the poly(arylene thioether-ketone) is held at 50°C. for 5 minutes in an inert gas atmosphere, heated to 420° C. at a rateof 75° C./min and then held for 10 minutes at 420° C.; and (c) reducedviscosity being 0.3-2 dl/g as determined by viscosity measurement at 25°C. and a polymer concentration of 0.5 g/dl in 98 percent by weightsulfuric acid; and optionally, (B) at least one component selected fromup to 100 parts by weight of at least one thermoplastic resin and up to15 parts by weight of at least one filler.
 2. The stretched film asclaimed in claim 1, wherein the poly(arylene thioether-ketone) has adensity of at least 1.34 g/cm³ at 25° C. when annealed at 280° C. for 30minutes.
 3. The stretched film as claimed in claim 1, wherein thepoly(arylene thioether-ketone) is an uncured polymer.
 4. The stretchedfilm as claimed in claim 1, wherein the thermoplastic resin is apoly(arylene thioether) having predominant recurring units of theformula ##STR9##
 5. The stretched film as claimed in claim 1, whereinthe thermoplastic resin is an aromatic polyether ketone.
 6. Thestretched film as claimed in claim 1, wherein the stretched film hasbeen stretched to a draw ratio of from 1.5:1 to 7:1 in at least oneaxial direction.
 7. The stretched film as claimed in claim 1, whereinthe stretched film has the following physical properties:(a) density ofportions of said poly(arylene thioether-ketone) being at least 1.34g/cm³ at 25° C.; (b) tensile strength being at least 5 kg/mm² at 23° C.or at least 1 kg/mm² at 270° C.; (c) tensile modulus being at least 200kg/mm² at 23° C. or at least 5 kg/mm² at 270° C.; and (d) temperature of10-seconds solder heat resistance being at least 280° C.
 8. Thestretched film as claimed in claim 1, wherein the coefficient of surfacedynamic friction of the stretched film as measured at 25° C. againstanother stretched film of the same kind as the first-mentioned stretchedfilm in accordance with the testing method of ASTM-D1894 is not greaterthan 0.7.
 9. The stretched film as claimed in claim 1, wherein thethermoplastic material is substantially free of the thermoplastic resin.10. The stretched film as claimed in claim 1, wherein the thermoplasticmaterial is substantially free of the filler.
 11. A stretchedpoly(arylene thioether-ketone) film made of a thermoplastic materialwhich has been stretched to a draw ratio of from 1.5:1 to 7:1 in atleast one axial direction and which comprises:(A) 100 parts by weight ofa melt-stable poly(arylene thioether-ketone) having predominantrecurring units of the formula ##STR10## wherein the --CO-- and --S--are in the para position to each other, and having the followingphysical properties (a)-(c):(a) melting point, Tm being 310-380° C.; (b)residual melt crystallization enthalpy, ΔHmc (420° C./10 min) being atleast 10 J/g, and melt crystallization temperature, Tmc (420° C./10 min)being at least 210° C., wherein ΔHmc (420° C./10 min) and Tmc (420°C./10 min) are determined by a differential scanning calorimeter at acooling rate of 10° C./min, after the poly(arylene thioether-ketone) isheld at 50° C. for 5 minutes in an inert gas atmosphere, heated to 420°C. at a rate of 75° C./min and then held for 10 minutes at 420° C.; and(c) reduced viscosity being 0.3-2 dl/g as determined by viscositymeasurement at 25° C. and a polymer concentration of 0.5 g/dl in 98percent by weight sulfuric acid; and optionally, (B) at least onecomponent selected from up to 100 parts by weight of at least onethermoplastic resin and up to 15 parts by weight of at least one filler.12. A stretched poly(arylene thioether-ketone) film made of athermoplastic material which has been stretched to a draw ratio of from1.5:1 to 7:1 in at least one axial direction and which comprises:(A) 100parts by weight of a melt-stable poly(arylene thioether-ketone) havingpredominant recurring units of the formula ##STR11## wherein the --CO--and --S-- are in the para position to each other, and having thefollowing physical properties (a)-(c):(a) melting point, Tm being310-380° C.; (b) residual melt crystallization enthalpy, ΔHmc (420°C./10 min) being at least 10 J/g, and melt crystallization temperature,Tmc (420° C./10 min) being at least 210° C., wherein ΔHmc (420° C./10min) and Tmc (420° C./10 min) are determined by a differential scanningcalorimeter at a cooling rate of 10° C./10 min, after the poly(arylenethioether-ketone) is held at 5020 C. for 5 minutes in an inert gasatmosphere, heated to 420° C. at a rate of 75° C./min and then held for10 minutes at 420° C.; and (c) reduced viscosity being 0.3-2 dl/g asdetermined by viscosity measurement at 25° C. and a polymerconcentration of 0.5 g/dl in 98 percent by weight sulfuric acid; andoptionally, (B) at least one component selected from up to 100 parts byweight of at least one thermoplastic resin and up to 15 parts by weightof at least one filler, wherein the stretched film has the followingphysical properties:(a) density of portions of said poly(arylenethioether-ketone) being at least 1.34 g/cm³ at 25° C.; (b) tensilestrength being at least 5 kg/mm² at 23° C. or at least 1 kg/mm² at 270°C.; (c) tensile modulus being at least 200 kg/mm² at 23° C. or at least5 kg/mm² at 270° C.; and (d) temperature of 10-seconds solder heatresistance being at least 280° C.